The present invention relates to a directivity diversity communication system, which reduces the influence of fading due to the multi-path of electromagnetic wave in a wireless communication. The present invention is useful, in particular, in a mobile communication system in which small equipment size is preferable.
In a conventional space diversity reception system, a pair of antennas 18 and 19 spaced (L) longer than several wavelengths have been utilized as shown in FIG. 1. In the figure, the reference numeral 20 is a conductor plane, 21 is a diversity reception circuit having a pair of antenna input branches 22 and 23. The input signals on the input branches 22 and 23 are combined or switched according to a conventional diversity technique, and the combined signal is detected in the receiver, which provides an output signal on the output terminal (OUT).
FIG. 2A shows a conventional antenna having the perpendicular directivities for a directivity diversity reception system, in which the reference numeral 18 is a first dipole antenna, 19 is a second dipole antenna which is positioned perpendicular to the first dipole antenna 18 as shown in the figure. In the figure, the symbols 22a and 22b are terminals of the first and the second antenna branches 22 and 23, respectively. The first and the second antennas 18 and 19 of FIG. 2A have the perpendicular directivities 24 and 25, respectively, as shown in FIG. 2B, and therefore, those two antenna elements 18 and 19 may be utilized for the antenna branches for a directivity diversity reception system.
However, the antennas and/or the diversity systems shown in FIG. 1 and/or FIG. 2A have the disadvantage that the area of space needed for mounting an antenna is extremely large, and each length of the area of space is longer than 1/2 wavelength, and therefore, a diversity communication system having that large antenna must be large in size, or an antenna must be installed in a space separated from a receiver housing. Therefore, a prior diversity communication system has not been preferable as a mobile communication system, in which a small sized communication system is desirable.
Further, a prior diversity communication system has the disadvantage that the structure is not sufficiently strong, due to the use of thin linear antennas which are easily broken.